Two-step orthogonal-state-based protocol of quantum secure direct communication with the help of order-rearrangement technique

TL;DR

This paper introduces a two-step quantum secure direct communication protocol using orthogonal states and order-rearrangement, enhancing security by limiting Eve's access to two-particle operations, and discusses differences from the GV protocol.

Contribution

It presents a novel two-particle protocol for quantum secure direct communication that leverages orthogonal states and order-rearrangement to improve security against eavesdropping.

Findings

Security relies on restricting Eve's two-particle operations.

Orthogonal states are partially distinguishable in the bipartite case.

Different information-disturbance trade-offs compared to GV protocol.

Abstract

The Goldenberg-Vaidman (GV) protocol for quantum key distribution (QKD) uses orthogonal encoding states of a particle. Its security arises because operations accessible to Eve are insufficient to distinguish the two states encoding the secret bit. We propose a two-particle cryptographic protocol for quantum secure direct communication, wherein orthogonal states encode the secret, and security arises from restricting Eve from accessing any two-particle operations. However, there is a non-trivial difference between the two cases. While the encoding states are perfectly indistinguishable in GV, they are partially distinguishable in the bi-partite case, leading to a qualitatively different kind of information-vs-disturbance trade-off and also options for Eve in the two cases.